The present invention relates to a sizing composition and sized glass fiber strand useful in reinforcing polymers.
More particularly the present invention relates to a sizing composition for glass fibers to produce sized glass fibers with improved performance in polymeric molding compounds.
Reinforced thermosetting plastics can be reinforced with several forms of glass fibers including roving, continuous strand, chopped fibers, mat, woven fabrics and the like. The reinforced thermosetting plastic composites can be produced from thermosetting molding compounds like bulk molding compounds and sheet molding compounds, that typically have about 15 to 25 and 25 to 45 percent glass content respectively. Two families of fiber glass reinforced molding sheets that have recently been commercialized are the XMC.RTM. composites and HMC.RTM. composites available from PPG Industries, Inc., Pittsburgh, Pa. These composites have high-strength for structural uses. The HMC.RTM. composite offers isotropic strength properties approaching twice those of conventional sheet molding compound by employing high glass fiber content with little or no filler. XMC.RTM. composite is a directionally oriented, moldable resin-glass fiber sheet containing 65 to 75 percent continuous reinforcement.
The glass fibers used as reinforcement for the thermosetting molding sheets are formed by being drawn at a high rate of speed from molten cones of glass from tips of small orifices in a platinum device called a bushing. In order to protect the glass fibers from interfilament abrasion during formation and further processing and to make them compatible with polymeric materials like the thermosetting materials, a sizing composition is applied to the glass fibers during their formation.
In order to form acceptable fiber glass reinforced molding composites, the glass fibers must have an acceptable sizing composition on their surface. The sizing compositions conventionally contain lubricants, film formers, coupling agents, wetting agents, emulsifiers, and the like. The solubility of the glass fiber sizing composition in ethylenically unsaturated organic solvents can affect the final properties of the molded product, because a myriad of applications of sized glass fibers in thermosetting molding composites utilize unsaturated polyesters or vinyl ester resins. In instances where severe shear is necessary to disperse the glass fibers through the polyester premix, it is desirable to have a sizing composition which is substantially insoluble or totally insoluble in the polyester resin premix to prevent filamentation of the strand, i.e., to keep the filaments in discreet bundles. For example, bulk molding compounds, which are chemically thickened premixed resins having a mixture of the resin and monomer with an inert filler, glass fiber reinforcement, a catalyst and possible other additives, are prepared by mixing the components in a high shear mixer. The unaged polyester monomer solution, having a thickening agent and other ingredients, have dispersed homogeneously throughout the resinous phase the chopped glass fiber strand or roving as glass fibers by the action of the high shear mixer. The bulk molding compound produced from the mixing after thickening on aging can be sliced into desired shapes such as cubes and the like and placed in a press to form articles of the desired design.
When severe shear is not necessary to homogeneously disperse the glass fiber strand throughout the polyester or vinyl ester premixed during compounding and molding, increased solubility of the sizing composition on the strand can be tolerated.
If the sizing composition on the glass fibers is not properly formulated, the fibers will not disperse uniformly throughout the resin premix. The characteristic of the molding compound formed from the polyester and glass fibers which describes the homogeneity of the premix composite is called "wet-through" or "flow-through". It is desirable to have a high degree of wet-through in a bulk molding compound, sheet molding compound, and the HMC.RTM. composites and the XMC.RTM. composites, in order that the final physical properties of the composites and the processibility thereof are at their maximum level.
On the other hand, it is also desirable that the glass fiber strand be wet-out during compounding which means that the resin encapsulates the glass fiber strands and no bare glass is visible throughout the formed molded compound. Wet-out during compounding is a measure of the apparent intimacy of contact between the resin matrix and the glass fiber strand. If the glass fiber strands are not immediately wet-out following compounding it is not expected that they will wet-out on aging due to the increase in the viscosity of the compound. This leads to adverse effects on the processibility, molding characteristics, and surface properties of the final molded article or composite.
It is the object of the present invention to provide a sizing composition to give glass fibers improved wet-through or flow-through properties and better or improved wet-out properties.
It is an additional object of the invention to provide a sizing composition which yields improved physical properties such as integrity between the glass fibers and the resin of a thermosetting molding compound in the production of thermosetting molding sheet composites.
It is a further additional object of the invention to provide a sizing composition which yields improved integrity between glass fibers and polyester, vinyl ester or epoxy resins where severe shear is necessary to disperse the glass fibers throughout the resin premix, for example, in the preparation of bulk molding compound.
It is another further object of the invention to provide sized glass fibers in the form of continuous strand, chopped fibers, mat, or roving and woven fabrics that have improved integrity, wet-out and wet-through in use for the preparation of reinforced thermosetting molding composites.
It is a further additional object of the invention to provide a sizing composition for glass fibers that yields sized glass fiber strands having improved integrity and reduced degradation in polyester resins, vinyl ester resins, and epoxy resins during the severe abuse experienced by the glass fibers during the injection process in the production of HMC.RTM. composites.
It is a further additional object of the present invention to provide sized glass fiber strands that can be used in reinforced thermosetting molding composites that leads to improved physical properties of the composites.